Cornish engine
at Cruquius, showing the beams of the pumping engine emerging from the supporting wall]] A Cornish engine is a type of steam engine developed in Cornwall, England, mainly for pumping water from a mine. It is a form of beam engine that uses steam at a higher pressure than the earlier engines designed by James Watt. The engines were also used for powering man engines to assist the underground miners' journeys to and from their working levels, for winching materials into and out of the mine and for powering the ore stamping machinery. The main characteristics of Cornish engines were: # the use of medium pressure steam (up to 50 psi), expansively, and # condensing the low pressure steam after expansion. # Other characteristics included insulation of steam lines and the cylinder, and steam jacketing the cylinder, both of which had previously been used by Watt. A Cornish engine pumps by a falling weight that is lifted by the engine. Few remain in their original locations, the majority having been scrapped when their related industrial firm closed. The Cornish engine developed irregular power throughout the cycle, completely pausing at one point while having rapid motion on the down stroke, making it unsuitable for rotary motion and most industrial applications. Background: the steam engine in Cornwall Cornwall has long had mines for tin, copper and other metal ores, but if mining is to take place below adit, means must be found of draining water from the mine. This may be done using horse power or a waterwheel to operate pumps, but horses have limited power and waterwheels need a suitable stream of water. Accordingly, the conversion of coal into power to work pumps was highly desirable to the mining industry. Wheal Vor (mine) had one of the earliest Newcomen engines before 1714, but Cornwall has no coalfield and coal imported from south Wales was expensive. The cost of fuel for pumping was thus a significant part of mining costs. This meant that many early Watt engines were erected by Boulton and Watt in Cornwall. They charged the mine owners a royalty based on a share of the fuel saving. The fuel efficiency of an engine was measured by its "duty", expressed in the work (in foot-pounds) generated by a bushel (94 pounds) of coal. Early Watt engines had a duty of 20 million, and later ones over 30 million. Development of the Cornish engine The Cornish engine depended on the use of steam pressure above atmospheric pressure, as devised by Richard Trevithick in the 19th century. Trevithick's early "puffer" engines discharged steam into the atmosphere. This differed from the Watt steam engine, which depended solely on the creation of a vacuum when steam was condensed. Trevithick's later ones (in the 1810s) combined the two principles, starting with high pressure steam but also condensing it in a separate condenser. In a parallel development Arthur Woolf developed the compound engine, in which the steam expanded in two cylinders successively. When Trevithick left for South America in 1816 he passed his patent rights for his latest invention to William Sims, who built (or adapted) a number of engines, including one at Wheal Chance (operating at 40 pounds per square inch above atmospheric pressure, which achieved a duty of nearly 50 million, but its duty then fell back. A test was carried out between a Trevithick type single-cylinder engine and a Woolf compound engine at Wheal Alfred in 1825, when both achieved a duty of slightly more than 40 million. The next improvement was achieved in the late 1820s by Samuel Grose, who decreased the heat loss by insulating the pipes, cylinders, and boilers of the engines, improving the duty to more than 60 million at Wheal Hope and later to almost 80 million at Wheal Towan. Nevertheless, the best duty was usually a short-lived achievement due to general deterioration of machinery, leaks from boilers, and the deterioration of boiler plates (meaning that pressure had to be reduced). Minor improvements increased the duty somewhat, but the engine seems to have reached its practical limits by the mid-1840s. With pressures of up to 50 psi, the shocks are likely to have caused machinery breakages. The same improvements in duty occurred in engines operating Cornish stamps and whims, but generally came slightly later. In both cases the best duty was lower than for pumping engines, particularly so for whim engines, whose work was discontinuous. The impetus for the improvement of the steam engine came from Cornwall because to the high price of coal there, but both capital and maintenance costs were higher than a Watt steam engine. This long delayed the installation of Cornish engines outside Cornwall. A second hand Cornish engine was installed at East London Waterworks in 1838, and compared to a Watt engine with favourable results, because the price of coal in London was even higher than in Cornwall. However, in the main textile manufacturing areas, such as Manchester and Leeds, the coal price was too low to make replacement economic. Only in the late 1830s did textile manufacturers begin moving to high pressure engines, usually by adding a high pressure cylinder, forming a compound engine, rather than following the usual Cornish practice. Preserved Cornish engines , housing a 30 inch engine]] Several Cornish engines are preserved in England. The Kew Bridge Steam Museum in London has the largest collection of Cornish engines in the world. At Crofton Pumping Station, in Wiltshire, a Grade 1 listed building houses two Cornish engines, one of which (the 1812 Boulton and Watt) is the "oldest working beam engine in the world still in its original engine house and capable of actually doing the job for which it was installed", that of pumping water to the summit pound of the Kennet and Avon Canal. Two examples also survive at the Cornish Mines and Engines museum on the site of East Pool mine near the town of Pool, Cornwall. The Cruquius pumping station in the Netherlands contains a Cornish engine with the largest diameter cylinder ever built for a Cornish engine, at 3.5 metre diameter (144 inches). The engine, which was built by Harvey & Co in Hayle, Cornwall, England, has eight beams connected to the one cylinder, each beam driving a single pump. The engine was restored to working order between 1985 and 2000, although it is now operated by an oil-filled hydraulic system, since restoration to live steam operating was not viable. See also *Beam engine *Mining in Devon and Cornwall *Stationary steam engine *Lean's Engine Reporter *Cataract (beam engine) References External links *Cornish beam engine animation *Cornish engines in Pool *Cruquius pumping station (includes mechanical details, simulations, technical drawings, etc.) Category:Cornish engines Category:Beam engines Category:Stationary steam engines Category:Steam engines Category:Mining in Cornwall Category:History of the steam engine